Preserving S1-AP UE contexts on SCTP failover

ABSTRACT

According to some embodiments, a method in a network node of a wireless communication network comprises determining that a plurality of S1-AP UE contexts maintained by the network node remain valid after a SCTP failure; generating an S1 Setup Request message comprising an indication that the UE contexts remain valid; and communicating the S1 Setup Request message to a MME. In particular embodiments, a method in an MME comprises receiving an S1 Setup Request message from a network node comprising an indication that UE contexts maintained by the network node remain valid after a SCTP failure. The MME determines a plurality of UE contexts maintained by the MME remain valid after a SCTP failure; generates an S1 Setup Response message comprising an indication that UE contexts maintained by the MME remain valid; and communicates the S1 Setup Response message to the network node.

TECHNICAL FIELD

Particular embodiments relate generally to signaling in wirelesscommunications networks, and more particularly to preserving S1Application Protocol (S1-AP) user equipment (UE) contexts on failover ofa Stream Control Transmission Protocol (SCTP) endpoint.

RELATED APPLICATION

This application claims benefit under 35 U.S.C. § 119(e) to U.S.Provisional Application Ser. No. 62/115,909, entitled “SCTP FAILOVERWHILE RETAINING S1-AP UE CONTEXTS,” filed Feb. 13, 2015, the entirecontent of which is incorporated herein by reference.

BACKGROUND

Third Generation Partnership Project (3GPP) defines the S1 interface forinterconnecting the evolved NodeB (eNB, eNodeB) component of the evolveduniversal terrestrial radio access network (E-UTRAN) to the core network(CN) of the evolved packet system (EPS). The E-UTRAN architectureconsists of a set of eNodeBs connected to the evolved packet core (EPC)through the S1 interface. The set of eNodeBs may include a Home eNodeB(HeNB) and a HeNB gateway (HeNB GW). For example, the S1-AP interfaceexists between the MME and the HeNB GW and the HeNB GW and the HeNB.Thus, the HeNB GW may perform the functionality of an MME or an eNodeB.As used herein, the term “eNodeB” may refer to an eNodeB or a HeNB GW,and the term “MME” may refer to an MME or a HeNB GW. The overall longterm evolution (LTE) architecture and E-UTRAN architecture are describedin 3GPP TS 36.401.

The S1 interface is specified at the boundary between the EPC and theE-UTRAN. From the S1 perspective, the E-UTRAN access point is an eNodeB,and the EPC access point is either the control plane mobility managemententity (MME) logical node or the user plane serving-gateway (S-GW)logical node. The Stream Control Transmission Protocol (SCTP), specifiedin IETF RFC 4960, is used to support the exchange of S1 ApplicationProtocol (S1-AP) signaling messages between an eNodeB and an MME.

One function of S1-AP is managing UE contexts (i.e., establishing andreleasing UE contexts in the eNodeB and in the EPC to support userindividual signaling on S1). The S1 UE context management functionsupports the establishment of the necessary overall initial UE contextincluding E-UTRAN Radio Access Bearer (E-RAB) context, security context,roaming and access restrictions, etc. The establishment of the overallinitial UE context is initiated by the MME. The S1 UE context managementfunction also supports the release of the context previously establishedin the eNodeB. The release of the context may be triggered by the MMEeither directly or following a request received from the eNodeB.

The eNodeB generally downloads most of its UE context information fromthe MME. The SCTP protocol provides IP level communication between theMME and eNodeB nodes and it transports the S1-AP messages. SCTP is usedfor reliable, in sequence delivery of messaging between the two SCTPendpoints for the duration of the link association. According to 3GPPspecifications, if the SCTP association is lost, then the eNodeB deletesall its UE contexts. The UEs perform Service Request procedures anddownload a UE context again from the MME in response to an S1-AP Setupmessage. This may, for example, result in audio disruption during aVoice over LTE call, or dropped video frames for a video stream.

Specifically, 3GPP TS 36.413 release 12 subclause 8.7.3.1 describes thatthe purpose of the S1 Setup procedure is to exchange application leveldata needed for the eNodeB and the MME to correctly interoperate on theS1 interface. Setup is the first S1-AP procedure triggered after thetransport network layer (TNL) association becomes operational. It usesnon-UE associated signaling. The setup procedure reinitializes theE-UTRAN S1-AP UE contexts (if any) and erases all related signalingconnections in the two nodes like a Reset procedure would do, and clearsMME overload state information at the eNodeB.

This behavior is appropriate when, for example, the eNodeB, MME, or HeNBGW experiences a failure in which it loses all SCTP and UE contextinformation. In other situations, however, such as when one processorperforms the SCTP functions and a different processor stores the UEcontext information, the behavior is inefficient. For example, a largeeNodeB, large HeNB BW, or MME may have 150,000 connected users.Resetting all the connections generates release, setup, and/or modifyrequest/responses for each connection. This could potentially add up toalmost a million messages traversing the network as part of an eNodeBreset.

One alternative is to replicate the SCTP state and all non-acknowledgeddata between two different processors. At high signaling rates, however,such replication requires enormous processing power and a two-phasecommit to replicate state data at both boards, which can beprohibitively expensive. Thus, in conventional systems, the SCTP statemay be lost on most hardware faults associated with the SCTP process.

As another alternative, some equipment vendors provide proprietaryimplementations that assume that if an eNodeB does not send an S1 Setupmessage, then the eNodeB preserved its UE contexts. Such animplementation ignores the 3GPP requirement that the S1 Setup message besent as the first message in a new SCTP connection. Another problem isthat the MME may autonomously delete an SCTP association and related UEcontexts because of an SCTP timeout at the MME, which results instranded UE contexts on the eNodeB. This may also result innon-responsive S1-AP connections to an MME when the MME is waiting foran S1 Setup before providing full service to an eNodeB. Thus, suchimplementations are unreliable because the circumstances of an SCTPrestart/setup may not be clear to each SCTP peer.

SUMMARY

According to some embodiments, method in a network node of a wirelesscommunication network comprises determining that a plurality of S1Application Protocol (S1-AP) user equipment (UE) contexts maintained bythe network node remain valid after a Stream Control TransmissionProtocol (SCTP) failure; generating an S1 Setup Request messagecomprising an indication that the plurality of UE contexts maintained bythe network node remain valid; and communicating the S1 Setup Requestmessage to a mobility management entity (MME). The MME is an SCTP peerof the network node.

In particular embodiments, the method further comprises receiving, fromthe MME, an S1 Setup Response message comprising an indication that aplurality of UE contexts maintained by the MME remain valid. The methodmay also comprise receiving, from the MME, an S1 Setup Response messagecomprising an indication that a plurality of UE contexts maintained bythe MME are invalid, and reinitializing the plurality of UE contextsmaintained by the network node.

In particular embodiments, the method further comprises determining thata UE context maintained by the network node is invalid after the SCTPfailure; generating an S1 Reset message comprising an indication of theinvalid S1-AP UE context; and communicating the S1 Reset message to theMME.

In particular embodiments, the indication that the plurality of UEcontexts maintained by the network node remain valid comprises a hashvalue identifying the plurality of UE contexts, such as one or moreHypertext Transfer Protocol (HTTP) entity tags (ETags).

According to some embodiments, a method in a MME of a wirelesscommunication network comprises receiving an S1 Setup Request messagefrom a network node. The S1 Setup Request message comprises anindication that a plurality of S1-AP UE contexts maintained by thenetwork node remain valid after a SCTP failure. The method furthercomprises determining whether a plurality of UE contexts maintained bythe MME remain valid after a SCTP failure.

In particular embodiments, the method further comprises, upondetermining the plurality of UE contexts maintained by the MME remainvalid after the SCTP failure, generating an S1 Setup Response messagecomprising an indication that the plurality of UE contexts maintained bythe MME remain valid; and communicating the S1 Setup Response message tothe network node. The method may further comprise, upon determining theplurality of UE contexts maintained by the MME are invalid after theSCTP failure, generating an S1 Setup Response message comprising anindication that the plurality of UE contexts maintained by the MME areinvalid; reinitializing the plurality of UE contexts maintained by theMME; and communicating the S1 Setup Response message to the networknode.

In particular embodiments, the indication that the plurality of UEcontexts maintained by the MME remain valid comprises a hash valueidentifying the plurality of UE contexts, such as one or more HTTPETags.

According to some embodiments, a network node comprises a detect liningmodule, a message generating module, and a communicating module. Thedetermining module is operable to determine that a plurality of S1-AP UEcontexts maintained by the network node remain valid after a SCTPfailure. The generating module is operable to generate an S1 SetupRequest message comprising an indication that the plurality of UEcontexts maintained by the network node remain valid. The communicatingmodule is operable to communicate the S1 Setup Request message to a MME.The MME is an SCTP peer of the network node.

According to some embodiments, a MME comprises a communicating moduleand a determining module. The communicating module is operable toreceive an S1 Setup Request message from a network node. The S1 SetupRequest message comprises an indication that a plurality of S1-AP UEcontexts maintained by the network node remain valid after a SCTPfailure. The determining module is operable to determine whether aplurality of UE contexts maintained by the MME remain valid after a SCTPfailure.

Also disclosed is a computer program product. The computer programproduct comprises instructions stored on non-transient computer-readablemedia which, when executed by a processor, perform the acts ofdetermining that a plurality of S1-AP UE contexts maintained by thenetwork node remain valid after a SCTP failure; generating an S1 SetupRequest message comprising an indication that the plurality of UEcontexts maintained by the network node remain valid; and communicatingthe S1 Setup Request message to a MME. The MME is an SCTP peer of thenetwork node.

Another computer program product comprises instructions stored onnon-transient computer-readable media which, when executed by aprocessor, perform the acts of receiving an S1 Setup Request messagefrom a network node. The S1 Setup Request message comprises anindication that a plurality of S1-AP UE contexts maintained by thenetwork node remain valid after a SCTP failure. The instructions, whenexecuted, also perform the act of determining whether a plurality of UEcontexts maintained by the MME remain valid after a SCTP failure.

Particular embodiments may exhibit some of the following technicaladvantages. In an S1 architecture where a first module performs SCTPprocessing and a second module stores S1-AP information, such as UEcontext information, a failure or restart of the SCTP module may notadversely impact UEs connected to the eNodeB and MME. For example, aparticular advantage is that SCTP failures may not interrupt audio,video, etc. connections for a UE connected to the MME (assuming otherrequired resources, such as radio transmitter, etc., are not impacted bythe SCTP module failure). Another advantage is more efficient use ofnetwork resources. For example, depending on the number of connectedUEs, resetting all S1 connections for an eNodeB may generate a largenumber of signaling messages. Thus, preventing an unnecessary reset ofall UE-associated logical S1 connections on an eNodeB may preventunnecessary signaling messages, which conserves network resources.

Another advantage is that particular embodiments are backward compatiblewith previous 3GPP implementations because a new optional informationelement may simply be ignored by previous implementations. For example,if either eNodeB or MME does not support the new information element,both sides may perform as a conventional system and reset the UEcontexts.

In particular embodiments, if either the eNodeB or the MME has deletedits SCTP associations and related UE contexts (e.g., based on a timeout,etc.), then the node may simply not include the new information elementin the Setup Request or Response message, causing the SCTP peer to alsoreset its UE contexts. Thus, preventing stranded UE contexts is anotheradvantage of particular embodiments.

As another advantage, in particular embodiments a first eNodeB may takeover for a second eNodeB if the first eNodeB has the UE contextinformation of the second eNodeB. For example, two Home eNodeB gatewaysmay share UE context information. Upon failure of one gateway, the othergateway may take over all the UE connections of the failed gateway.Other technical advantages will be readily apparent to one skilled inthe art from the following figures, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments and their featuresand advantages, reference is now made to the following description,taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating an example wireless network,according to a particular embodiment;

FIG. 2 is a block diagram illustrating an example SCTP network node,according to particular embodiment;

FIG. 3A is an example signaling diagram for SCTP setup between a networknode and an MME, according to particular embodiments;

FIG. 3B illustrates an example S1 Setup Request message, according toparticular embodiments;

FIG. 3C illustrates an example S1 Setup Response message, according toparticular embodiments;

FIG. 4 is a flow diagram of a method in a network node of preservingS1-AP contexts on SCTP failover, according to particular embodiments;

FIG. 5 is a flow diagram of a method in an MME of preserving S1-APcontexts on SCTP failover, according to particular embodiments;

FIG. 6A is a block diagram illustrating an example embodiment of anetwork node;

FIG. 6B is a block diagram illustrating example of components of anetwork node;

FIG. 7A is a block diagram illustrating an example embodiment of an MME;

FIG. 7B is a block diagram illustrating example of components of an MME.

DETAILED DESCRIPTION

Resetting all S1 connections after failure of a network node's SCTPmodule may interrupt user traffic, and may adversely impact networksignaling traffic because of the large amount of signaling informationexchanged to re-establish the S1 connections. An object of the presentdisclosure is to obviate at least these disadvantages by providingefficient recovery from an SCTP module failure and minimize interruptionof user traffic. Network nodes that separate their SCTP module fromtheir UE context storage may benefit from particular embodiments.

For example, embodiments described herein are directed to methods andsystems configured to replace or modify the S1 Setup procedure in 3GPPto include a flag that indicates UE contexts are preserved after afailure (i.e., only the SCTP module has failed/restarted and the S1-APUE context information is retained). Particular embodiments include aflag to indicate a network node was able to preserve its UE contextsafter a failure.

For example, a particular embodiment includes an S1-AP Setup Requestmessage with an optional information element (IE) indicating that the UEcontexts were preserved at the eNodeB. An S1-AP Setup Response messageincludes an optional IE indicating the UE contexts were preserved at theMME. If the MME receives a Setup Request from the eNodeB including thenew IE, and the MME has also retained its UE contexts, then the MMEincludes the new IE in the S1 Setup Response message sent back to theeNodeB. The new information element (i.e., flag) indicates to both nodesthat most UE contexts have been saved. Both nodes may continue withoutdeleting and re-establishing all their UE contexts. If either sideexcludes this new IE, then both sides may assume most UE contexts havebeen lost and perform conventional S1 Setup behavior.

During an SCTP failure, some SCTP data chunks may not get deliveredwhich could result in a few UEs in a state that does not match their UEcontext. In particular embodiments, these mismatched UE contexts areidentified and the network node will send an S1 Reset message for themismatched UEs.

In particular embodiments, the new IE comprises a single bit in theS1-AP message. The single bit may comprise a Boolean flag that indicateswhether the UE contexts are preserved. In some embodiments, the new IEcomprises multiple hits which can be used to provide more informationthan just the Boolean value. For example, multiple bits may represent ahash value used to compare whether the UE contexts are the same on eachnetwork node.

The following description sets forth numerous specific details. It isunderstood, however, that embodiments may be practiced without thesespecific details. In other instances, well-known circuits, structuresand techniques have not been shown in detail in order not to obscure theunderstanding of this description. Those of ordinary skill in the art,with the included descriptions, will be able to implement appropriatefunctionality without undue experimentation.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to implement such feature, structure, orcharacteristic in connection with other embodiments, whether or notexplicitly described.

Particular embodiments are described with reference to FIGS. 1-7B of thedrawings, like numerals being used for like and corresponding parts ofthe various drawings. LTE is used throughout this disclosure as anexample cellular system, but the ideas presented herein may apply toother wireless communication systems as well.

FIG. 1 is a block diagram illustrating an example wireless network,according to a particular embodiment. Wireless network 100 includes oneor more wireless devices 110 (such as mobile phones, smart phones,laptop computers, tablet computers, MTC devices, or any other devicesthat can provide wireless communication) and a plurality of radionetwork nodes. Wireless device 110 may also be referred to as a UE. Thenetwork nodes include network nodes 120 (such as base stations oreNodeBs), and a core network node 130 (such as an MME). Radio networknode 120 serves coverage area 115 (also referred to as cell 115).

In general, wireless devices 110 that are within coverage of radionetwork node 120 (e.g., within cell 115 served by network node 120)communicate with radio network node 120 by transmitting and receivingwireless signals 140. For example, wireless devices 110 and radionetwork node 120 may communicate wireless signals 140 containing voicetraffic, data traffic, and/or control signals. A network node 120communicating voice traffic, data traffic, and/or control signals towireless device 110 may be referred to as a serving network node 120 forthe wireless device 110. Wireless signals 140 may include both downlinktransmissions (from radio network node 120 to wireless devices 110) anduplink transmissions (from wireless devices 110 to radio network node120).

Each network node 120 may have a single transmitter or multipletransmitters for transmitting signals 140 to wireless devices 110. Insome embodiments, network node 120 may comprise a multi-inputmulti-output (MIMO) system. Similarly, each wireless device 110 may havea single receiver or multiple receivers for receiving signals 140 fromnetwork nodes 120.

Core network node 130 manages the establishment of communicationsessions and various other functionality for wireless communicationdevices 110 within coverage (or partial coverage) of the wirelessnetwork. The network nodes connect through interconnecting network 125,which refers to any interconnecting system capable of transmittingaudio, video, signals, data, messages, or any combination of thepreceding.

In particular embodiments, core network node 130 comprises MME 130. S1interfaces 150 connect MME 130 to network nodes 120. The S1-AP providessignaling between network node 120 and MME 130 over S1 interface 150.S1-AP uses SCTP to transport S1-AP signaling messages between networknode 120 and MME 130.

One function of S1-AP is managing UE contexts (i.e., establishing andreleasing UE contexts for wireless devices 110 in network node 120 andin MME 130 to support user individual signaling on S1). Theestablishment of the initial UE context is initiated by MME 130. The S1UE context management function also supports the release of the contextpreviously established in network node 120. The release of the contextmay be triggered by MME 130 either directly or following a requestreceived from network node 120. Network node 120 generally downloadsmost of its UE context information from MME 130. In particularembodiments, a UE context refers to any S1 information associated with aparticular UE. A particular example of a UE context is described in 3GPPTS 36.413.

In wireless network 100, each radio network node 120 may use anysuitable radio access technology, such as long term evolution (LTE),LTE-Advanced, UMTS, HSPA, GSM, cdma2000, WiMax, WiFi, and/or othersuitable radio access technology. Wireless network 100 may include anysuitable combination of one or more radio access technologies. Forpurposes of example, various embodiments may be described within thecontext of certain radio access technologies. However, the scope of thedisclosure is not limited to the examples and other embodiments coulduse different radio access technologies.

As described above, embodiments of a wireless network may include one ormore wireless devices and one or more different types of radio networknodes capable of communicating with the wireless devices. The networkmay also include any additional elements suitable to supportcommunication between wireless devices or between a wireless device andanother communication device (such as a landline telephone). A wirelessdevice may include any suitable combination of hardware and/or software.For example, in particular embodiments, a network node may include anysuitable combination of hardware and/or software. For example, inparticular embodiments, a network node, such as network node 120, mayinclude the components described with respect to FIG. 6A below. Asanother example, in particular embodiments a core network node, such asMME 130, may include the components described with respect to FIG. 7Abelow.

FIG. 2 is a block diagram illustrating an example SCTP network node,according to particular embodiment. SCTP network node 210 may compriseany of the network nodes described with respect to FIG. 1, such asnetwork node 120 and MME 130. SCTP network node 210 includes SCTP module212 and UE context storage module 214.

SCTP module 212 includes any suitable combination of hardware andsoftware for providing SCTP functionality for SCTP network node 210. Inparticular embodiments, SCTP module 212 may comprise only software. Inparticular embodiments, SCTP module 212 may comprise multiple SCTPmodules 212 that provide redundancy for each other. For example, failureof one SCTP module 212 may result in another SCTP module 212 taking overand providing SCTP functionality for SCTP network node 210.

UE context storage module 214 includes any suitable combination ofhardware and software for storing UE contexts for SCTP network node 210.In particular embodiments, UE context storage module 214 may compriseonly software. In particular embodiments, UE context storage module 214may comprise multiple UE context storage modules 214 that provideredundancy for each other. For example, failure of one UE contextstorage module 214 may result in another UE context storage module 214taking over and providing UE context storage functionality for SCTPnetwork node 210.

In particular embodiments, SCTP module 212 is in communication with UEcontext storage module 214. SCTP module 212 may communicate UE contextinformation to UE context storage module 214, and vice versa.Communication between SCTP module 212 and UE context storage module 214may comprise any suitable inter-process, inter-task, inter-thread, etc.communication.

In particular embodiments, UE context storage module 214 and SCTP module212 may comprise separate processors, boards, cards, controllers, etc.In particular embodiments, UE context storage module 214 and SCTP module212 may comprise the same processor, board, card, controller, etc.

Under particular operating conditions, SCTP module 212 may fail orrestart without adversely impacting UE context storage module 214. Forexample, SCTP module 212 may comprise a separate processor than UEcontext storage module 214. Failure or restart of the SCTP module 212processor will not adversely impact UE context storage module 214because UE context storage module 214 comprises a processor independentfrom SCTP module 212. In other embodiments, SCTP module 212 and UEcontext storage module 214 may comprise software processes on the sameprocessor. SCTP module 212 may fail and restart (e.g., failure of SCTPsoftware stack, network failure, etc.) without adversely impacting UEcontext storage module 214. Thus, under particular circumstances UEcontext storage module 214 may preserve UE context information for useby SCTP module 212 after a failure and restart.

In particular embodiments, SCTP module 212 of network node 120 may failwithout adversely impacting S1-AP information, such as UE contextinformation stored by UE context storage module 214. Thus, instead ofreinitializing all UE contexts upon restart of SCTP module 212, networknode 120 may use the preserved UE context information when SCTP module212 restarts.

In particular embodiments, network node 120 may include a flag in theSetup Request Message that indicates UE contexts are preserved after afailure. Similarly, MME 130 may include a flag in the Setup Responsemessage that indicates UE contexts are preserved after a failure.

In particular embodiments, an SCTP failure may refer to any event thatresults in the restart or reinitialization of the SCTP protocol stack.For example, failures may include hardware failures, software failures,network failures, or any event that disrupts normal SCTP operation.

FIG. 3A is an example signaling diagram for SCTP setup between a networknode and an MME, according to particular embodiments. In particularembodiments, one or more steps of the signaling diagram may be performedby components of wireless network 100 described with reference to FIGS.1 and 2. For example, FIG. 3A illustrates an example SCTP setup betweennetwork node 120 a and MME 130.

Setup is the first S1-AP procedure triggered after the TNL associationbecomes operational. At 312, network node 120 a sends a S1 Setup Requestmessage to MME 130. The S1 Setup Request message transfers informationfor a TNL session to MME 130. In particular embodiments, network node120 a may determine it can use a plurality of its existing UE contexts.Network node 120 a may include a flag in the S1 Setup Request messageindicating that network node 120 a does not need to delete its existingUE contexts.

MME 130 receives the S1 Setup Request message. If MME 130 is unable todetect the flag or if the flag is not present, then MME 130 may deleteits UE contexts. If MME 130 detects the flag is present, then MME 130may determine whether it can use any of its existing UE contexts.

At 314, MME 130 sends a S1 Setup Response message to network node 120 a.The S1 Setup Response message transfers information for a TNL session tonetwork node 120 a. In particular embodiments, MME 130 may include aflag in the S1 Setup Response message indicating that MME 130 will notdelete its existing UE contexts.

FIG. 3B illustrates an example S1 Setup Request message, according toparticular embodiments. S1 Setup Request message 320 may includeoptional information element 322.

Information element 322 is an optional information element thatindicates a network node, such as network node 120, can use its existingUE context information. For example, information element 322 mayindicate that a plurality of UE contexts maintained by network node 120remain valid after an SCTP failure. In particular embodiments,information element 322 comprises a single bit. The single bit maycomprise a Boolean flag representing whether the network node can useits existing UE context information. For example, if network node 120determines that after a restart of its SCTP protocol stack network node120 can use a plurality of its existing UE contexts, then network node120 may include information element 322 in S1 Setup Request message 320.In other embodiments, information element 322 may comprise any number ofbits.

For example, in particular embodiments information element 322 mayinclude a number of bits for security purposes. Information element 322may serve as both a flag indicating that network node 120 may use itsexisting UE contexts as well as a way to verify the identity of networknode 120. An advantage of such an embodiment is that it may providesecurity against an SCTP peer hijacking other nodes UE contexts, eitherintentionally or unintentionally.

In particular embodiments, information element 322 may include a hashvalue representing the contents of the network node's UE contexts. Forexample, in particular embodiments information element 322 may simplyinclude a version number. In other embodiments information element 322may include the result of a hash function applied to all the UE contextsof the network node. In particular embodiments, information element 322may include one or more HTTP ETags. Including two information elements322 may facilitate graceful handling of particular race conditions byincluding an old hash value (such as an old ETag) and a new hash value(such as a new ETag).

A particular advantage is that the described embodiments may be usedwhen the IP addresses of the new SCTP association are different than theold IP addresses. For example, an S1-AP proxy, such as a Home eNodeBGateway, may take over the UE connection of another Home eNodeB Gateway.

FIG. 3C illustrates an example S1 Setup Response message, according toparticular embodiments. S1 Setup Response message 330 may includeoptional information element 332.

Information element 332 is an optional information element thatindicates a network node, such as MME 130, can use its existing UEcontext information. For example, information element 332 may indicatethat a plurality of UE contexts maintained by MME 130 remain valid afteran SCTP failure. In particular embodiments, information element 332comprises a single bit. As described above with respect to informationelement 322 in FIG. 3B, information element 332 may comprise a singlebit or any number of bits, including version numbers, hash values,ETags, etc. Information element 332 represents whether an MME can useits existing UE context information. For example, if MME 130 determinesthat after a restart of its SCTP protocol stack MME 130 can use aplurality of its existing UE contexts, then MME 130 may includeinformation element 332 in S1 Setup Response message 330.

FIG. 4 is a flow diagram of a method in a network node of preservingS1-AP contexts on SCTP failover, according to particular embodiments. Inparticular embodiments, one or more steps of method 400 may be performedby components of wireless network 100 described with reference to FIGS.1-7B.

The method begins at step 412, where a network node determines that aplurality of UE contexts maintained by the network node remain validafter a SCTP failure. For example, network node 120 may determine thatits SCTP module experienced a failure and restarted. As part of therestart, network node 120 may determine that it includes a number of UEcontexts for UE connections that existed before the SCTP failure.Network node 120 may determine that a large number of the UE contextsare still valid and usable. According to particular embodiments, not allUE contexts need be valid. Advantages of the described embodiments maystill be realized even if some UE contexts are later reset.

At step 414, the network node generates an S1 Setup Request messagecomprising an indication that the plurality of UE contexts maintained bythe network node remain valid. For example, network node 120 a maygenerate S1 Setup Request message 320 including information element 322.

In particular embodiments, generating the S1 Setup Request message mayinclude performing a hash function, or some other validation function,on the UE contexts of network node 120, or generating an identifier ofnetwork node 120, as part of generating information element 322.

At step 416, the network node communicates the S1 Setup Request messageto a MME. For example, network node 120 a may communicate S1 SetupRequest message 320 (including information element 322) to MME 130.

At step 418, the network node receives a S1 Setup Response message fromthe MME. For example, network node 120 a may receive S1 Setup Responsemessage 330 from MME 130.

In particular embodiments, the network node determines whether the MMEincludes valid and usable UE contexts. For example, network node 120 amay inspect S1 Setup Response message 330 for information element 332.

In particular embodiments, if information element 332 is not present, ifinformation element 332 indicates MME 130 does not have valid UEcontexts, if information element 332 indicates MME 130 has valid UEcontexts but the UE contexts do not match the UE contexts of networknode 120 a, or if any other suitable criteria is not satisfied, thennetwork node 120 a may continue to step 420 an reinitialize its UEcontexts according to conventional S1 Setup procedure.

In particular embodiments, if information element 332 is present andindicates that MME 130 has valid UE contexts, then network node 120 amay continue to step 422 where network node 120 a continues its S1 Setupprocedure using its existing UE contexts.

In particular embodiments, network node 120 a may compare receivedinformation element 332 with sent information element 322. For example,information element 322 may contain an ETag representing the UE contextsof network node 120 a. Information element 332 may contain an ETagrepresenting the UE contexts of MME 130. Network node 120 a may comparethe two ETags to verify the information stored at MME 130 matches theinformation stored at network node 120 a. In particular embodiments,network nodes may include two ETags in the Setup messages. For example,one ETag may represent the UE context information before a failure eventand one may represent the UE context information after the failureevent.

In particular embodiments, network node 120 a may transmitidentification, validation, or authentication information in informationelement 322. Network node 120 a may receive identification, validation,or authentication information in information element 332. Network node120 a may use any suitable information from information element 332 todetermine whether to continue to either step 420 or 422.

In some circumstances, a small number of UE contexts may be invalidafter an SCTP failure. For example, during the time of the SCTP failurethe protocol may have been unstable resulting in some failed connections(e.g., some SCTP data chunks may have been lost, resulting in a statemismatch). In these circumstances, some embodiments transition these UEsinto an EPS connection management (ECM) idle state at both the MME andthe network node.

Particular embodiments may determine which connections need to be resetby tracking any UE contexts that are incompletely deactivated in thepast M seconds (e.g., S1 context release without an answer). Particularembodiments may use the list to send an S1-AP Reset message with theassociated UE context after the Setup procedure. UE contexts may beidentified by 32 bit IDs (MME UE S1-AP ID IE and eNB UE S1-AP ID IE),and the S1-AP Reset message may include multiple IDs in each message,resulting in an efficient reset of the few unusable connections.

Modifications, additions, or omissions may be made to method 400.Additionally, one or more steps in method 400 of FIG. 4 may be performedin parallel or in any suitable order.

FIG. 5 is a flow diagram of a method in an MME of preserving S1-APcontexts on SCTP failover, according to particular embodiments. Inparticular embodiments, one or more steps of method 500 may be performedby components of wireless network 100 described with reference to FIGS.1-7B.

The method begins at step 512, where a MME receives an S1 Setup Requestcomprising an indication that a plurality of UE contexts maintained bythe network node remain valid after a SCTP failure. For example, MME 130may receive S1 Setup Request message 320 including information element322 from network node 120 a, such as the message sent by network node120 a described with respect to step 416 of FIG. 4.

At step 514, the MME determines whether its UE contexts are valid. Forexample, MME 130 may determine that its SCTP module experienced afailure and restarted. As part of the restart, MME 130 may determinethat it includes a number of UE contexts for UE connections that existedbefore the SCTP failure. MME 130 may determine that a large number ofthe UE contexts are still valid and usable. According to particularembodiments, not all UE contexts need be valid.

In particular embodiments, MME 130 may not be aware of an SCTP failure.For example, in response to receiving information element 322, MME 130may simply verify whether it has any valid UE contexts.

In particular embodiments, MME 130 may confirm identification,validation, or authentication information included in informationelement 322. For example, MME 130 may compare an ETag received ininformation element 322 with an ETag generated based on the UE contextsof MME 130.

If the MME determines its UE contexts are valid, and optionally verifiesany information received from the network node, then the MME maycontinue to step 516 where it generates an S1 Setup Response messagecomprising an indication that a plurality of the UE contexts maintainedat the MME remain valid. For example, MME 130 may generate S1 SetupResponse message 330 including information element 332.

In particular embodiments, generating the S1 Setup Response message mayinclude performing a hash function, or some other validation function,on the UE contexts of MME 130, or generating an identifier of MME 130,as part of generating information element 332.

If the MME does not recognize the information element in the S1 SetupRequest message, does not validate the information element in the S1Setup Request message, does not have a plurality of valid UE contexts,or does not satisfy any other suitable criteria, then the MME maycontinue to step 518 where it generates an S1 Setup Response messagecomprising an indication that a plurality of the UE contexts maintainedat the MME are not valid. For example, MME 130 may generate S1 SetupResponse message 330 including information element 332 indicating the UEcontexts are not valid. In other embodiments, MME 130 may generate S1Setup Response message 330 that does not include information element332. The absence of information element 332 may indicate that the UEcontexts for the MME are not valid.

At step 520, the MME reinitializes its UE contexts. For example, MME 130may reinitialize its UE contexts.

At step 522, the MME communicates the S1 Setup Response message to thenetwork node. For example, MME 130 may communicate S1 Setup Responsemessage 330 to network node 120 a.

Modifications, additions, or omissions may be made to method 500.Additionally, one or more steps in method 500 of FIG. 5 may be performedin parallel or in any suitable order.

A particular advantage of the embodiments described above are that theyprovide backwards compatibility with previous 3GPP network equipmentbecause the new, optional information element may be ignored if it isnot supported (e.g., if either node does not support certain features,all UE contexts may be deleted according to conventional S1 Setupbehavior). For supported nodes, excluding the information element foreither side also solves the problem described above where the either theMME or eNodeB has deleted all its UE contexts because of an SCTP linkfailure being detected before the SCTP link has been reestablished.

In other embodiments, an eNodeB that restarts SCTP may send an S1-APConfiguration Update message to indicate that the eNodeB preserved itsUE contexts. If the MME accepts the configuration update, then the MMEaccepts the UE context. Similarly, an MME that restarts SCTP may send anS1-AP Configuration Update message to indicate it preserved its UEcontexts. Particular embodiments may define a new message, such as UEContext Preserved, to signal the same information.

FIG. 6A is a block diagram illustrating an example embodiment of anetwork node. Network node 120 can be an eNodeB, a nodeB, a basestation, a wireless access point (e.g., a Wi-Fi access point), a lowpower node, a base transceiver station (BTS), a transmission point ornode, a remote RF unit (RRU), a remote radio head (RRH), or other radioaccess node. Network node 120 includes at least one transceiver 610, atleast one processor 620, at least one memory 630, and at least onenetwork interface 640. Transceiver 610 facilitates transmitting wirelesssignals to and receiving wireless signals from a wireless device, suchas wireless devices 110 (e.g., via an antenna); processor 620 executesinstructions to provide some or all of the functionality described aboveas being provided by a network node 120; memory 630 stores theinstructions executed by processor 620; and network interface 640communicates signals to backend network components, such as a gateway,switch, router, Internet, Public Switched Telephone Network (PSTN),controller, and/or other network nodes 120.

Processor 620 includes any suitable combination of hardware and softwareimplemented in one or more integrated circuits or modules to executeinstructions and manipulate data to perform some or all of the describedfunctions of the network node. In some embodiments, processor 620 mayinclude, for example, one or more computers, one more programmable logicdevices, one or more central processing units (CPUs), one or moremicroprocessors, one or more applications, and/or other logic, and/orany suitable combination of the preceding. Processor 620 may includeanalog and/or digital circuitry configured to perform some or all of thedescribed functions of network node 120. For example, processor 620 mayinclude resistors, capacitors, inductors, transistors, diodes, and/orany other suitable circuit components.

Memory 630 is generally operable to store computer executable code anddata. Examples of memory 630 include computer memory (e.g., RandomAccess Memory (RAM) or Read Only Memory (ROM)), mass storage media(e.g., a hard disk), removable storage media (e.g., a Compact Disk (CD)or a Digital Video Disk (DVD)), and/or or any other volatile ornon-volatile, non-transitory computer-readable and/orcomputer-executable memory devices that store information.

In some embodiments, network interface 640 is communicatively coupled toprocessor 620 and refers to any suitable device operable to receiveinput for network node 120, send output from network node 120, performsuitable processing of the input or output or both, communicate to otherdevices, or any combination of the preceding. Network interface 640includes appropriate hardware (e.g., port, modem, network interfacecard, etc.) and software, including protocol conversion and dataprocessing capabilities, to communicate through a network.

In particular embodiments, processor 620 in communication with networkinterface 640 determines whether a network node's S1 UE contexts remainvalid after an SCTP failure and/or restart, generates S1 messages, suchas S1 Setup Request message 320, and communicates S1 messages with MME130, such as S1 Setup Request message 320 and S1 Setup Response message330.

Other embodiments of network node 120 include additional components(beyond those shown in FIG. 6A) responsible for providing certainaspects of the network node's functionality, including any of thefunctionality described above and/or any additional functionality(including any functionality necessary to support the solution describedabove). The various different types of radio network nodes may includecomponents having the same physical hardware but configured (e.g., viaprogramming) to support different radio access technologies, or mayrepresent partly or entirely different physical components.

FIG. 6B is a block diagram illustrating example components of a networknode 120. The components may include a determining module 650, a messagegenerating module 660, and communicating module 670.

Determining module 650 may perform the processing functions of networknode 120 related to determining whether S1 UE contexts are valid afteran SCTP failure. In certain embodiments, determining module 650 mayinclude or be included in processor 620. Determining module 650 mayinclude analog and/or digital circuitry configured to perform any of thefunctions of determining module 650 and/or processor 620. In particularembodiments, determining module 650 may communicate with messagegenerating module 660 and communicating module 670.

Message generating module 660 may perform the message generatingfunctions of network node 120 related to generating S1 Setup messagesand their information elements, such as S1 Setup Request message 320 andinformation element 322. In certain embodiments, message generatingmodule 660 may include or be included in processor 620. Messagegenerating module 660 may include analog and/or digital circuitryconfigured to perform any of the functions of message generating module660 and/or processor 620. In particular embodiments, message generatingmodule 660 may communicate with determining module 650 and communicatingmodule 670.

Communicating module 670 may perform the communicating functions ofnetwork node 120 related to communicating S1 messages with MME 130. Inparticular embodiments, communicating module 670 may communicate, to MME130, S1 Setup Request message 320 including information element 322. Incertain embodiments, communicating module 670 may include or be includedin processor 620. Communicating module 670 may include analog and/ordigital circuitry configured to perform any of the functions ofcommunicating module 670 and/or processor 620. In particularembodiments, communicating module 670 may also communicate withdetermining module 650 and message generating module 660.

FIG. 7A is a block diagram illustrating an example embodiment of an MME.MME 130 includes processor 720, memory 730, and network interface 710.In some embodiments, processor 720 executes instructions to provide someor all of the functionality described above as being provided by theMME, memory 730 stores the instructions executed by processor 720, andnetwork interface 710 communicates signals to any suitable node, such asa gateway, switch, router, Internet, Public Switched Telephone Network(PSTN), network nodes 120, other MME 130, etc.

Processor 720 may include any suitable combination of hardware andsoftware implemented in one or more modules to execute instructions andmanipulate data to perform some or all of the described functions of theMME 130. In some embodiments, processor 720 may include, for example,one or more computers, one or more central processing units (CPUs), oneor more microprocessors, one or more applications, and/or other logic.

Memory 730 is generally operable to store instructions, such as acomputer program, software, an application including one or more oflogic, rules, algorithms, code, tables, etc. and/or other instructionscapable of being executed by a processor. Examples of memory 730 includecomputer memory (for example, Random Access Memory (RAM) or Read OnlyMemory (ROM)), mass storage media (for example, a hard disk), removablestorage media (for example, a Compact Disk (CD) or a Digital Video Disk(DVD)), and/or or any other volatile or non-volatile, non-transitorycomputer-readable and/or computer-executable memory devices that storeinformation.

In some embodiments, network interface 710 is communicatively coupled toprocessor 720 and may refer to any suitable device operable to receiveinput for the MME, send output from the MME, perform suitable processingof the input or output or both, communicate to other devices, or anycombination of the preceding. Network interface 710 may includeappropriate hardware (e.g., port, modem, network interface card, etc.)and software, including protocol conversion and data processingcapabilities, to communicate through a network.

In particular embodiments, processor 720 in communication with networkinterface 710 determines whether an MME's S1 UE contexts remain validafter an SCTP failure and/or restart, generates S1 messages, such as S1Setup Response message 330, and communicates S1 messages with networknode 120, such as S1 Setup Request message 320 and S1 Setup Responsemessage 330.

Other embodiments of the network node may include additional componentsbeyond those shown in FIG. 7A that may be responsible for providingcertain aspects of the MME's functionality, including any of thefunctionality described above and/or any additional functionality(including any functionality necessary to support the solution describedabove).

FIG. 7B is a block diagram illustrating example of components of an MME.The components may include a determining module 760, a messagegenerating module 770, and communicating module 760.

Determining module 760 may perform the processing functions of MME 130related to determining whether S1 UE contexts are valid after an SCTPfailure. In certain embodiments, determining module 760 may include orbe included in processor 720. Determining module 760 may include analogand/or digital circuitry configured to perform any of the functions ofdetermining module 760 and/or processor 720. In particular embodiments,determining module 760 may communicate with message generating module770 and communicating module 750.

Message generating module 770 may perform the message generatingfunctions of MME 130 related to generating S1 Setup messages and theirinformation elements, such as S1 Setup Response message 330 andinformation element 332. In certain embodiments, message generatingmodule 770 may include or be included in processor 720. Messagegenerating module 770 may include analog and/or digital circuitryconfigured to perform any of the functions of message generating module770 and/or processor 720. In particular embodiments, message generatingmodule 770 may communicate with determining module 760 and communicatingmodule 750.

Communicating module 750 may perform the communicating functions ofnetwork MME 130 related to communicating S1 messages with network node120. In particular embodiments, communicating module 750 maycommunicate, to network node 120, S1 Setup Response message 330including information element 332. In certain embodiments, communicatingmodule 750 may include or be included in processor 720. Communicatingmodule 750 may include analog and/or digital circuitry configured toperform any of the functions of communicating module 750 and/orprocessor 720. In particular embodiments, communicating module 750 mayalso communicate with determining module 760 and message generatingmodule 770.

Some embodiments of the disclosure may provide one or more technicaladvantages. As an example, in some embodiments a failure or restart of anetwork node's SCTP module may not impact UEs connected to the eNodeBand MME. For example, a particular advantage is that SCTP failures maynot interrupt audio, video, etc. connections for a UE connected to theMME (assuming other required resources, such as radio transmitter, etc.,are not impacted by the SCTP module failure). Another advantage is moreefficient use of network resources. For example, resetting all S1connections for an eNodeB may generate a large number of signalingmessages. Preventing an unnecessary reset of all UE-associated logicalS1 connections on an eNodeB may prevent unnecessary signaling messages,thus conserving network resources.

As another advantage, in particular embodiments a first eNodeB may takeover for a second eNodeB if the first eNodeB has the UE contextinformation of the second eNodeB. For example, two Home eNodeB gatewaysmay share UE context information. Upon failure of one gateway, the othergateway may take over all the UE connections of the failed gateway.

Some embodiments may benefit from some, none, or all of theseadvantages. Other technical advantages may be readily ascertained by oneof ordinary skill in the art.

Modifications, additions, or omissions may be made to the systems andapparatuses disclosed herein without departing from the scope of theinvention. The components of the systems and apparatuses may beintegrated or separated. Moreover, the operations of the systems andapparatuses may be performed by more, fewer, or other components.Additionally, operations of the systems and apparatuses may be performedusing any suitable logic comprising software, hardware, and/or otherlogic. As used in this document, “each” refers to each member of a setor each member of a subset of a set.

Modifications, additions, or omissions may be made to the methodsdisclosed herein without departing from the scope of the invention. Themethods may include more, fewer, or other steps. Additionally, steps maybe performed in any suitable order.

Although this disclosure has been described in terms of certainembodiments, alterations and permutations of the embodiments will beapparent to those skilled in the art. Accordingly, the above descriptionof the embodiments does not constrain this disclosure. Other changes,substitutions, and alterations are possible without departing from thespirit and scope of this disclosure, as defined by the claims below.

Abbreviations used in the preceding description include:

3GPP Third Generation Partnership Project

BTS Base Transceiver Station

CN Core Network

D2D Device-to-Device

ECM EPS Connection Management

eNB eNodeB

EPC Evolved Packet Core

EPS Evolved Packet System

E-RAB E-UTRAN Radio Access Bearer

E-UTRAN Evolved Universal Terrestrial Radio Access Network

HeNB Home eNodeB

HeNB GW Home eNodeB Gateway

IE Information Element

LTE Long Term Evolution

M2M Machine to Machine

MME Mobility Management Entity

RAN Radio Access Network

RAT Radio Access Technology

RRH Remote Radio Head

RRU Remote Radio Unit

S1-AP S1 Application Protocol

SCTP Stream Control Transmission Protocol

S-GW Serving Gateway

TNL Transport Network Layer

UE User Equipment

WAN Wireless Access Network

The invention claimed is:
 1. A method in a network node of a wirelesscommunication network, the method comprising: determining that aplurality of S1 Application Protocol (S1-AP) user equipment (UE)contexts maintained by the network node remain valid after a StreamControl Transmission Protocol (SCTP) failure; generating an S1 SetupRequest message comprising an indication that the plurality of UEcontexts maintained by the network node remain valid; and communicatingthe S1 Setup Request message to a mobility management entity (MME), theMME an SCTP peer of the network node.
 2. The method of claim 1, furthercomprising receiving, from the MME, an S1 Setup Response messagecomprising an indication that a plurality of UE contexts maintained bythe MME remain valid.
 3. The method of claim 1, further comprising:receiving, from the MME, an S1 Setup Response message comprising anindication that a plurality of UE contexts maintained by the MME areinvalid; and reinitializing the plurality of UE contexts maintained bythe network node.
 4. The method of claim 1, further comprising:determining a UE context maintained by the network node is invalid afterthe SCTP failure; generating an S1 Reset message comprising anindication of the invalid S1-AP UE context; and communicating the S1Reset message to the MME.
 5. The method of claim 1, wherein theindication that the plurality of UE contexts maintained by the networknode remain valid comprises a hash value identifying the plurality of UEcontexts.
 6. The method of claim 1, wherein the indication that theplurality of UE contexts maintained by the network node remain validcomprises one or more Hypertext Transfer Protocol (HTTP) entity tags(ETags).
 7. A method in a mobility management entity (MME) of a wirelesscommunication network, the method comprising: receiving an S1 SetupRequest message from a network node, the S1 Setup Request messagecomprising an indication that a plurality of S1 Application Protocol(S1-AP) user equipment (UE) contexts maintained by the network noderemain valid after a Stream Control Transmission Protocol (SCTP)failure; and determining whether a plurality of UE contexts maintainedby the MME remain valid after a SCTP failure.
 8. The method of claim 7,further comprising: upon determining the plurality of UE contextsmaintained by the MME remain valid after the SCTP failure, generating anS1 Setup Response message comprising an indication that the plurality ofUE contexts maintained by the MME remain valid; and communicating the S1Setup Response message to the network node.
 9. The method of claim 7,further comprising: upon determining the plurality of UE contextsmaintained by the MME are invalid after the SCTP failure, generating anS1 Setup Response message comprising an indication that the plurality ofUE contexts maintained by the MME are invalid; reinitializing theplurality of UE contexts maintained by the MME; and communicating the S1Setup Response message to the network node.
 10. The method of claim 7,wherein the indication that the plurality of UE contexts maintained bythe MME remain valid comprises a hash value identifying the plurality ofUE contexts.
 11. The method of claim 7, wherein the indication that theplurality of UE contexts maintained by MME remain valid comprises one ormore Hypertext Transfer Protocol (HTTP) entity tags (ETags).
 12. Anetwork node comprising a processor operable to: determine that aplurality of S1 Application Protocol (S1-AP) user equipment (UE)contexts maintained by the network node remain valid after a StreamControl Transmission Protocol (SCTP) failure; generate an S1 SetupRequest message comprising an indication that the plurality of UEcontexts maintained by the network node remain valid; and communicatethe S1 Setup Request message to a mobility management entity (MME), theMME an SCTP peer of the network node.
 13. The network node of claim 12,the processor further operable to receive, from the MME, an S1 SetupResponse message comprising an indication that a plurality of UEcontexts maintained by the MME remain valid.
 14. The network node ofclaim 12, the processor further operable to: receive, from the MME, anS1 Setup Response message comprising an indication that a plurality ofUE contexts maintained by the MME are invalid; and reinitialize theplurality of UE contexts maintained by the network node.
 15. The networknode of claim 12, the processor further operable to: determine a UEcontext maintained by the network node is invalid after the SCTPfailure; generate an S1 Reset message comprising an indication of theinvalid S1-AP UE context; and communicate the S1 Reset message to theMME.
 16. The network node of claim 12, wherein the indication that theplurality of UE contexts maintained by the network node remain validcomprises a hash value identifying the plurality of UE contexts.
 17. Thenetwork node of claim 12, wherein the indication that the plurality ofUE contexts maintained by the network node remain valid comprises one ormore Hypertext Transfer Protocol (HTTP) entity tags (ETags).
 18. Amobility management entity (MME) comprising a processor operable to:receive an S1 Setup Request message from a network node, the S1 SetupRequest message comprising an indication that a plurality of S1Application Protocol (S1-AP) user equipment (UE) contexts maintained bythe network node remain valid after a Stream Control TransmissionProtocol (SCTP) failure; and determine whether a plurality of UEcontexts maintained by the MME remain valid after a SCTP failure. 19.The MME of claim 18, the processor further operable to: upon determiningthe plurality of UE contexts maintained by the MME remain valid afterthe SCTP failure, generate an S1 Setup Response message comprising anindication that the plurality of UE contexts maintained by the MMEremain valid; and communicate the S1 Setup Response message to thenetwork node.
 20. The MME of claim 18, the processor further operableto: upon determining the plurality of UE contexts maintained by the MMEare invalid after the SCTP failure, generate an S1 Setup Responsemessage comprising an indication that the plurality of UE contextsmaintained by the MME are invalid; reinitialize the plurality of UEcontexts maintained by the MME; and communicate the S1 Setup Responsemessage to the network node.
 21. The MME of claim 18, wherein theindication that the plurality of UE contexts maintained by the MMEremain valid comprises a hash value identifying the plurality of UEcontexts.
 22. The MME of claim 18, wherein the indication that theplurality of UE contexts maintained by MME remain valid comprises one ormore Hypertext Transfer Protocol (HTTP) entity tags (ETags).